In this study, longitudinal data from 708 schools across five states in the continental United States were analyzed to measure the time between initial training and adequate implementation of Tier I Schoolwide Positive Behavioral Interventions and Supports over 5 years and the extent to which it varied by school characteristics. Results indicated that, all else constant: elementary schools were more likely to reach adequate implementation before middle and high schools, non-Title I schools were more likely to reach adequate implementation before Title I schools, and suburban schools were more likely to reach adequate implementation before city schools. The findings provide empirical documentation of the average length of time required for adequate implementation of a systems-level intervention, as well as how that length differs across nonmalleable school characteristics.